Critical conditions were obtained for a series of uranium-graphite fueled assemblies in the C/Oy range 150 to 500 with thick graphite reflectors and Be or D2O islands. Perturbations were studied in order to find the effect on reactivity of geometrical changes and engineering features. Information from these studies was used to develop a mock-up of an optimum reactor geometry for the first rocket reactor test device, Kiwi-A. Studies on a zero power mock-up (Zepo-A) helped establish its design details. A cold critical check was made of the Kiwi-A reactor.

Two methods are described for the quantitative determination of vanadium in uranium-vanadium alloys. A procedure is also described for the quantitative determination of vanadium and chromium in uranium-chromium-vanadium alloys.

The index of refraction of PuO2 made by thermal decomposition of PU(C2O2, 6H2O gradually increases from a value < 1.9 to 2.40 as the decomposition temperature is increased from 150 degree to l000 degree C. This change in refractive index parallels a gradual change in the x-ray diffraction pattern from weak, diffuse lines for PuO2 ignited at 150° to sharp, well resolved lines for PuO2 ignited at 1000°C. Similar results are observed for PuO2 made by thermal decomposition of Pu2(C2O4)3*11H2O. The refractive index of PuO2 made from Pu metal at 170°C is 2.40 and is not affected by further ignition at higher temperatures, although crystal growth does occur. The rate of solution of PuO2 in an HCl-KI solution is greatest for samples prepared at low temperatures and decreases markedly for oxides ignited at higher temperatures. These observations hive been interpreted to mean that ignition at higher temperatures causes a gradual perfection of the originally highly distorted and impurity-containing PuO2 lattice obtained by low temperature decomposition of the oxalates and promotes the slow growth of crystallites. Both factors decrease the reactivity of the PuO2.

With the assumption of infinite conductivity a simple model may be constructed for the dynamic construction of a current carrying plasma, i.e., the pinch effect. The magneto-hydrodynamic equations of this model are discussed and solved. It is also shown that the infinite conductivity model can be derived from a picture of particles orbiting without collisions in the fields set up by their motions.

A spectrophotometric method used in the determination of thorium was modified for the purpose of analyzing plutonium alloys which contained 0.01 to 0.8 percent thorium. Absorbance values were measured at 545 millimicrons for solutions containing thorium and thorin, the organic reagent added to form a colored complex with thorium in the presence of plutonium (III) . With plutonium-thorium 0.8 percent thorium, the average recovery of thorium was 99.6 +- 1.5 percent. For similar samples containing 0.01 to 0.2 percent thorium, the average recovery 101.0 +- 3.4 percent, after the thorium was separated from plutonium by precipitation of thorium fluoride with the aid of lanthanum fluoride as a carrier.

The conductivity of ionized gases is treated by a method similar to that used by Alfven in his book "Cosmical Electrodynamics". The results differ from those of Alfven. In particular, it is shown that Alfven's conclusion, that whenever the Hall current disappears the conductivity becomes independent of the magnetic field, is not true in general. Moreover, it is not true under just the conditions of interest for the "Pinch Effect". The main conclusions of the present paper are (1) of currents down a tube, the ion component is the small fraction of m/M of the electron current, regardless of the magnitude of the magnetic field; (2) the conduction along the tube depends on the transverse motion of neutral mass, i.e. on the radial velocity of u(r) of the gas in the tube.

A spherical, unreflected U-235 critical assembly (52.6 kg) has been in operation since August, 1951. A remotely controlled mechanical system is used to assemble subcritical components of the sphere, and reactivity is adjusted with U-235 control rods positioned in the sphere. The maximum power level during sustained operation is about 1 kilowatt. In addition to investigations of the neutron spectrum of the assembly, observation of the changes of reactivity produced by inserting foreign materials into the assembly, and the dletermination of parameters such as the temperature coefficient of reactivity, studies have been made of the behavior of the assembly at reactivities above prompt critical.

A method is presented for determining heat transfer rates and thermal stresses from the gamma-ray energy absorption of nuclear reactor shells for plane, cylindrical, and spherical geometries. Criteria for minimizing thermal stresses are developed, along with the corresponding external cooling rates necessary to minimize the thermal stress. Design charts are presented for rapid determination of approximate thermal stresses and heat transfer rates, along with a numerical example illustrating the use of the charts..

The yield and energy distribution of the lower-energy neutrons resulting from interaction of 14-Mev neutrons with Li6 and Li7 have been measured in the energy range between 4 and 12 Mev. A coincidence spectrometer was used to detect the neutrons from a scatterer in the form of a spherical shell placed around the neutron source. By use of the spectrometer as a threshold detector, transmission measurements were also made, from which could be determined the elastic cross section for scattered neutrons above 12 Mev. The result is in agreement with the measurement of Graves of the amount of small-angle elastic scattering. Using the known total cross section of Li6, the known reaction cross sections, and the present measurements, a complete “audit” of the interacted neutrons is made. Qualitatively, one-half of the total cross section is due to small-angle elastic scattering, and all inelastic processes result in lower energy neutrons spread rather uniformly in the region from zero to 12 Mev. Measurement using a thin iron sphere gave a neutron spectrum in good agreement with previous results of Graves and Rosen.

A criticality equation is derived assuming slowing-down only by hydrogen. The use of criticality experiments as a basis for calculation is described. Approximate methods are given for handling inharmonicities and multi-region reactors. Some criticality data on solutions of U03 dissolved in H3PO4 are listed in Appendix 1, and the Goertzel-Selengut equations are derived in Appendix II.

A method for determining zirconium in plutonium-zirconium alloys was required as part of an investigation of alloys containing fissionable material, with possible use in nuclear reactors. Alloys of these two elements were brought into solution with a bisulfate fusion and the zirconium was separated by precipitation with p-bromomandelic acid. Determinations were completed by weighing the zirconium oxide obtained after ignition of the precipitate at 925 degree C. The precision of this recommended procedure was estimated in terms of the standard deviation for quadruplicate determinations, made with weight aliquots from dissolved alloy samples. The range for the standard deviation was 0.5 to 1.7 parts per thousand for samples from which aliquots each containing 9 to 15 mg of zirconium were selected. The complete recovery of zirconium from solutions of pure zirconyl chloride and plutonium trichloride was shown by the 95 percent confidence limits of 99.9 +- 0.3 percent for the average of four determinations, observed with samples containing 5 to12 mg of zirconium in the presence of 10 to 20 mg of plutonium. It was found the Mo, La, PU(III), and K2Cr2O7 do not interfere with zirconium determinations made according to the recommended procedures, but Pu(IV) does interfere slightly. It was …

Bismuth analytical methods were investigated for the purpose of selecting procedures which are satisfactory for the analysis of solutions containing plutonium and bismuth. The gravimetric procedure which is recommended for samples containing these two elements includes removal of the plutonium by peroxide precipitation, separation of the bismuth by precipitation with sodium carbonate, and final ignition of the bismuth as a phosphate. Necessary equipment and experimental technique are described. In the analysis of eight known samples by the recommended method, the average recovery of bismuth was 99.76 percent, with a standard deviation of 0.22 percent. The known samples contained about 35 mg of bismuth and 25 mg of plutonium. For similar samples in routine work, the confidence limits at the 95 percent level for the average of triplicated determinations are +- 0.30 percent of the bismuth in the the sample. Other methods investigated and having possible application for some Pu-Bi analysis problems include electrodeposition of bismuth on a mercury cathode and gravimetric analysis with BiCr(CNS)6 as the weighed product.

Determination of cadmium in plutonium-cadmium solutions was successfully accomplished by separating the plutonium as an insoluble peroxide, evaporating the solution containing the cadmium, and weighing the latter as a sulfate. with 5 t0 20 mg of cadmium and similar amounts of plutonium, the 95% confidence limits for the average of triplicate determinations was to be +- 0.3 percent of the cadmium in the sample. When samples contained as little as 5 mg of cadmium, it was necessary to correct the weight of cadmium sulfate with a carefully determined reagent blank which originated mainly from the action of hydrogen peroxide on glass containers.

Tests made on the Oy-Tu reacting assembly at Pajarito indicate that the lateral displacement of two halves of the active material within the assembly can be used as a control mechanism on this type of reacting assembly. This report describes a reacting assembly using a rotary control mechanism based on this principle and indicates the sensitivity of control possible with such a device.

Abstract: A five-crystal scintillation gamma-ray spectrometer was constructed for use as a Compton coincidence spectrometer or as a pair coincidence spectrometer. Preliminary tests are discussed. The efficiency in either mode of operation was found to be low; however, the backgrounds were favorable and good definition of characteristic lines was achieved...Future tests and plans for improvements are discussed."

Abstract: "A description of the instrumentation for neutron flux measurement from Kiwi-A at NTS is given as some discussion of start-up considerations, detector design, system response adjustments, and power calibration of the reactor at some low level of power."

From abstract: "A general and systematic development of reactor computing methods and detailed application given in Report LAMS-2255 separately is supplemented in this report for a few specific systems of interest to the Rover program. Neutron cross sections, reactor description, and computed results are given for a reactor required to have a constant (radially) power distribution at high temperatures."

Abstract: "The leakage neutron spectrum of a U²³³ spherical critical assembly (Jezebel) has been measured using nuclear emulsions as radiator and detector. The spectrum obtained is compared with similar measurements on the U-235 and Pu-239 analogues of Jezebel U²³³; it is found to agree closely with that of the Pu-239 assembly and to be harder than that of the U-235 assembly. All three spectra are compared with theoretical spectra obtained from a numerical approximation to the neutron transport equation."

Abstract: "The calculation of the efficiency of the Los Alamos hydrogen bubble chamber for detection of neutrons in the energy range 5 to 35 MeV has been done using a "Monte Carlo" technique. The detection efficiency is calculated as a function of energy of the neutron and angle of the proton recoil."